Without a doubt - Nike Air Presto shoes worn with thin socks. They are the most comfy shoes I've ever had in my life. I used to get horrible blisters at WDW and my feet would just kill me, but these shoes are all mesh and allow my feet to breathe and not get so sweaty. I've been four times since I've had them and I've only had one pinky-toe blister and it didn't hurt. I wear these shoes all the time now and my feet are totally spoiled. I have four pairs - two in use and two being saved for future trips.
www.finishline.com has a whole bunch of these on clearance (women's anyway) for $19.99, originally cost between $85 and $100. Some are really flashy - I have the white/silver/gray ones and they look pretty good with shorts, jeans, capris, etc.
I used to have to put about 5 waterproof bandaids on my heels before I found Sketchers slip-on tennis shoes. They are GREAT! And I love the fact that I can slip them off when sitting at a show to rest my tootsies. I was afraid the first time I wore them that they would slip while walking or running, but they don't. I have two pair and I really wear them out.
I like my New Balance walking shoes - style 609. I'm on my second pair now, after literally wearing out the first pair because I wore them almost daily. I'd like to try Tevas because I hear they're super-comfy, but I haven't found a pair yet that I like enough to shell out the $$.
My favorite shoes are Birkenstocks. Even when I am not on vacation if I have worn any other shoes all day I can't wait to change into my Birks. If you are looking for a bargain on them you can purchase Birkenstocks through QVC either online or on TV when they are being featured. I bought mine from them and I think they were less than $50.
This is a link to the American Podiatric Medical Association Web site's Seal of Accpetance where you can see footware products that are approved by the APMA. Pretty helpful when you are looking for good footware.
Adidas (great arch support) walking shoes with mesh sides and sport socks with ribbing at the arch to stop slipping - this combo first tried at WDW in 2000 and has worked on vacations w/walking elsewhere since (also neosporined toes and lots of minty footpowder - or is that too much info)
My Ecco Cosmos sandals. I used to get blisters every trip with my walking sneakers and cool max socks and antipersperant and now with my sandals...NO BLISTERS!
My Reebok DMX walking sneakers, you feel like you are walking on pillows! I also use the Spenco arch supports inside and my feet never hurt me, even after spending the entire day at the parks.